Theemo-detectom



THERMQ-DETECTii-R Thomas W. Bland and Lester A. fiBrie-n, use, alili Application September 1, 1953, Serial No. 377,832

4 Claims. (Cl. filth-4%) This invention relates to detector devices for fire alarms and more particularly to a thermo-detector for use on both open and closed circuits.

It is the primary object of this invention to provide a thermo-detectcr for use in fire alarm systems which employs a dual set of contacts so that it may be introduced into either an open or closed circuit fire alarm system.

it is a further object of this invention to provide a de tector device which operates on both a temperature rise and upon a fiXed temperature basis.

it is a still further object of this invention to provide a detector which is simple, yet positive, in its operation in a fire alarm system, which may be economically produced in large quantities and may be inserted into existing fire alarm systems without a major change in the existing system, but rather involves only a simple connection to be incorporated into the existing fire alarm system.

it is yet another object of this invention to provide in the detector device, a metered air escape preventing a false alarm due to normal temperature rises of the surrounding atmosphere.

Other objects and advantages will become apparent from the following detail description, forming the specification, and taken in conjunction with the accompanying drawings, wherein:

Figure l is a top plan View of the thermo-detector embodying this invention;

Figure 2 is a side elevational view thereof;

Figure 3 is an end View thereof; and

Figure 4 is a cross sectional View taken on line 4-4 of Figure 3.

As seen in Figures 1 to 3, the thermo-detector of this invention comprises a generally rectangular base iii and a generally dome-shaped air chamber housing 12. The base it? may be made of any suitable material, but is particularly adapted for molding operation when made of a suitable plastic material, while the housing 12 may be made of any suitable, thoroughly rigid, moldable material including the plastic material groups. The shape of both the housing and the base may be varied at will, the shapes illustrated in the drawings being indicative of only one application in regard to the geometric form thereof. The base it) is provided with a pair of mounting screw holes 14- and 16 adjacent opposite edges of the base for receiving screws or similar securing devices so that the base may be mounted upon a surface. The top surface upon which the housing 12 is mounted is provided with a central aperture 29 in which is slidably received a contact operating plunger 22. An annular recess 26 concentric with the aperture 26 is provided with internal threads and receives a threaded plug therein, the plug being indicated at 26. The plug 26 is provided with a central aperture which is in register with the aperture 2-9 in the top surface it; of the base it so that the plunger 22 may be slidably received therein. A plunger spring 3%} is placed within the aperture 23 so as to resiliently urge the plunger 22 against a diaphragm 32 extending arcuately across the interior of the housing 12. It will be noted that the plug tinited States Patent See 26 is removable from the lower or bottom surface of the base 10 and the flange 34 of the plug 26 is in contact with a recess 36 formed in the bottom surface 19 of the base 19.

The plunger 22 has a laterally extending arm 33 which projects into an inner recess 40 formed in the base 10 and carries a pair of contacts 42 and 44 on opposite sides of the arm and at the terminal or free end of the arm 38. Preferably, the plunger 22 and its associated integrally formed arm 38 is made of a non-conductive material, such as a suitable plastic. A conductor 46 connects the contact 42 with a terminal post or connecting screw 48 and a similar conductor 50 connects the contact 44 with a terminal post or connection screw 52 so that the posts or connection screws may be in turn introduced into an electrical circuit of an associated fire alarm system. A pair of spaced contacts 54 and 56 are disposed within the recess ii in oppositely disposed aligned relation and adapted to be in contact with one of the contacts carried by the arm A lead or conductor 5% places the contact 5 in communication with the connecting screw or terminal as while a similar lead wire or conductor 62 connects the contact 56 with the terminal or connecting screw 64 so that either of the terminals and 64 may be tied into an existing associated fire alarm system.

it will be noted from Figure 4, that the contact 42 is in engagement with the contact 54 since the plunger 22 which carries the contact is urged by the spring in a direction toward the housing 12. If the fire alarm system into which the thermo-detector of this invention is to be introduced is of the closed circuit type, then the terminal will be connected into the associated system While if the associated fire alarm system is of the open circuit type, then the system will be tied to the terminal that the thermo-detector may be readily incorporated into either an existing open or closed circuit associated fire alarm system since the terminal 6r) will provide a closed circuit as the contact 42. is in engagement with the ccntac 54. Since the contact 56 is spaced from the contact normally, an associated fire alarm system having an open circuit will be tied into the terminal 64 so as to maintain the circuit as an open circuit.

As previously indicated, the end of the plunger 22 remote from the spring 39 is in abutting relation with the diaphragm 32 and forced into such abutting contact by the resilient bias of the spring As the surrounding air about the housing 12 becomes heated, the air in the chamher 13 provided by the interior or" the housing 12 will become heated and expand forcing the diaphragm to move the plunger 22 against the spring 3%, consequently carrying the arm 33 also away from the diaphragm 32 and breaking the contact between contact 42 and contact 54 and thereby opening the normally closed circuit which will set oii the associated fire alarm system. The foregoing is of course assuming that the system has been of the closed circuit type and has been tied into the terminal If, however, the associated fire alarm system is of open circuit type ar the terminal connected thereto, then the plunger 22 upon further movement caused by expansion of the air in the chain er bring the contact into engagement with the contact thereby closing the normally open circuit to set the associated fire alarm into operation.

it will be noted that the diaphragn is of generally arcuate sha e and its peripheral portions of consid erably heavier construction t 1 portion which is in contact with the o 2 so that mov ment of the central portion of the di: n 33 will be achieved with a great deal less air expansion in the chamber 13 than would be the case if the diaphra m were of equal thickness throughout its entire extent.

As a fire breaks out, the air surrounding the housing 12 Will be generally heated rather rapidly thus causing the expansion of the air therein and the consequent movement of the diaphragm 32 and the plunger 22 to set the associated fire alarm system in operation as hereinbefore set forth. However, in some cases the fire may be of the type that starts gradually and builds in intensity so that only gradual expansion of the air in the chamber 13 will be effected. In the latter instance, a diaphragm 32 may not move as desired, but an auxiliary plunger operating device is incorporated into the present thermodetector. This auxiliary device, generally indicated at as, comprises a spring as extending within the air chamber 13 and disposed directly above 7 the central portion of the diaphragm 32 which is in abutting contact with the plunger 22. A spring retainer 7% carries an enlarged head '72 at one end thereof while the retainer passes centrally through the spring 68 and has its other end secured to the top of the housing 12 by a low meltin spring retainer button 74 so as to hold the spring under compression it its centrally disposed position above the plunger 22. The button '74 is of a material having a low but predetermined melting point so that when the surrounding air about the housing 12 becomes sufiiciently heated, the button 74 Will melt and the spring which is held under compression will thereby be released so as to strike the top of the central portion or" the diaphragm 32 forcing the plunger 22 into the aperture 28 in the plug 26, thus moving the contact 42 away from the contact 54 and moving the contact 44 into engagement with the contact 56 so as to set cit the associated fire alarm system into which the present thermo-detector is incorporated.

In order to prevent false alarms due to the normal rise in the surrounding temperature, a metered air escape '76, which is a passage transversely through the base it} and places the chamber 13 in communication with the atmosphere, is provided. The amount of air escaping through the passage '76 can be predetermined by providing a passage of lesser or greater cross sectional area.

From the foregoing, it will be seen that there has been provided a thermo-detector which may be incorporated into either a closed or open circuit fire alarm system and which is operable either by a change in the surrounding atmosphere rising in heat intensity or operative upon a fixed temperature basis so that a positive action will result in case of fire and the associated fire alarm wiil be placed in operation to give warning of the fire.

With regard to the air chamber housing 12, it should be noted that the lower periphery thereof is joined to the upper surface it; of the base It as at 73 so that the air chamber 13 defined by the housing 12 will be closed to the atmosphere except for the air escape passage 76. Also, it should be borne in mind that the terminal 43 is connected into an associated closed circuit type fire alarm system circuit along with the connection of the terminal ed into this circuit while the terminal 52 is connected into an open circuit type fire alarm system circuit along with the connection of the terminal 64 into this open circuit system.

Basically, the thermo-detector hereinbefore described, is adapted to be connected into the circuit of a fire alarm system, which system may be electrical and of the open or closed circuit type, and has a spring biased contact means in the nature of the plunger 22 carrying the contact arm 38 which in turn carries the contacts 42 and 44, this spring biased contact means being mounted for movement in a rectilinear path being urged in one direction along said path by the spring 30. The diaphragm means 32 is adapted to move in a path intersecting the rectilinear path of movement of the contact means and is responsive to a rate of temperature rise so as to engage the contact means and move it so as to energize the fire alarm circuit into which the thermodetector has been connected; and also, there is provided a fixed temperature means or device 66, of an auxiliary nature which is mounted in the rectilinear path of movement of the contact means but spaced therefrom and this fixed temperature device adapted to move in the rectilinear path when a predetermined atmospheric temperature is reached. So that in a single device, there is a diaphragm, or rate of temperature rise device, and a fixed temperature device, both of which are adapted to move a contact means so as to energize an electrical circuit of an associated fire alarm system to place the system in operation.

While there is shown and described the preferred embodiment of the invention, it is to be understood that the structure is susceptible to change and modification within the practicability of the invention and therefore should be limited only by the scope of the claims appended hereto.

What is claimed is:

l. A thermo-detector for electrical fire alarm devices comprising a base having a recess formed therein, a housing defining an air chamber, a diaphragm in said air chamber, a spring biased plunger carrying electrical contacts and normally urged into abutting relation with said diaphragm, a pair of spaced contacts to be disposed in said recess in the base carried by said base adjacent said contacts carried by said plunger and having one of the spaced contacts in engagement with said plunger carried contact, said diaphragm movable on expansion of the air in said chamber to force said plunger against its spring to move the contact carried by said plunger from its contacting relation with one of said spaced contacts into engaging relation with the other of said spaced contacts so as to cause the fire alarm device to operate.

2. A thermo-detector for open or closed circuit electrical fire alarm systems comprising a base and an air chamber carried on said base, the interior of said housing defining an air chamber, a diaphragm within said chamber, a spring biased contact arm operatively engaging said diaphragm and carrying a pair of oppositely disposed contacts thereon for connection into a fire alarm system, a pair of spaced contacts and a pair of terminals carried by said base, each or" said spaced contacts connected to one of said terminals, one of said arm carried contacts urged into engagement with one of said spaced contacts by the spring biased arm adapted to actuate a closed circuit fire alarm system being connected into the terminal connected to said one spaced contact in engagement With one of said arm carried contacts or to actuate an open circuit fire alarm system being connected to the other of said terminals connected to the other of said spaced contacs spaced from the other of said arm carried contacts, expansion of air in said chamber flexing said diaphragm to move said spring biased contact means so that said one contact carried thereby will be moved out of engagement with said one spaced contact and bring into engagement the other of said arm carried contacts and said other spaced contact whereby the fire alarm system into which said detector is connected will be set in operation.

3. A thermo-detector for open or closed circuit electrical fire alarm systems comprising a base and an air chamber carried on said base, the interior of said housing defining an air chamber, a diaphragm within said chamber, a spring biased contact arm operatively engaging said diaphragm and carrying a pair of oppositely disposed contacts thereon for connection into a fire alarm system, a pair of spaced contacts and a pair of terminals carried by said base, each of said spaced contacts connected to one of said terminals, one of said arm carried contacts urged into engagement with one of said spaced contacts by the spring biased arm adapted to actuate a closed circuit fire alarm system being connected into the terminal connected to said one spaced contact in engagement with one of said arm carried contacts or to actuate an open circuit fire alarm system being connected to the other of said terminals connected to the other of said spaced contacts spaced from the other of said arm carried contacts, expansion of air in said chamber flexing said diaphragm to move said spring biased contact means so that said one contact carried thereby will be moved out of engagement with said one spaced contact and bring into engagement the other of said arm carried contacts and said other spaced contact whereby the fire alarm system into which said detector is connected will be set in operation, and a metered air escape in said base communicating the air chamber with the atmosphere to permit a predetermined amount of air to escape from said chamber so as to prevent a false alarm due to gradual expansion of air in said chamber due to normal atmospheric conditions.

4. A thermo-detector for open or closed circuit electrical fire alarm systems comprising a base and an air chamber carried on said base, the interior of said housing defining an air chamber, a diaphragm within said chamber, a spring biased contact arm operatively engaging said diaphragm and carrying a pair of oppositely disposed contacts thereon for connection into a fire alarm system, a pair of spaced contacts and a pair of terminals carried by said base, each of said spaced contacts connected to one of said terminals, one of said arm carried contacts urged into engagement with one of said spaced contacts by the spring biased arm adapted to actuate a closed circuit fire alarm system being connected into the terminal connected to said one spaced contact in engagement with one of said arm carried contacts or to actuate an open circuit fire alarm system being connected to the other of said terminals connected to the other of said spaced contacts spaced from the other of said arm carried contacts, expansion of air in said chamber flexing said diaphragm to move said spring biased contact means so that said one contact carried thereby will be moved out of engagement with said one spaced contact and bring into engagement the other of said arm carried contacts and said other spaced contact whereby the fire alarm system into which said detector is connected will be set in operation, and an auxiliary fixed temperature device carried by said housing adapted to move said spring biased contact arm as the air temperature surrounding said housing reaches a predetermined value.

References Cited in the file of this patent UNITED STATES PATENTS 2,224,738 Lowe Dec. 10, 1940 2,267,484 Van Houten Dec. 23, 1941 2,272,864 Baak Feb. 10, 1942 2,275,949 Evans Mar. 10, 1942 

